1. Field of the Invention
The object of the invention is a multiple channel pipetting device as well as an exchangeable pipette shaft for a pipetting device.
2. Description of Related Art
The known multiple channel pipetting device, on which the invention is based (U.S. Pat. No. 3,855,868) is suitable for small stand distances of individual, neighboring pipette tips, in particular, for the low stand distances required in so-called micro titration stands. In order to be able to implement these small stand distances, the pipette shafts of this multiple channel pipetting device are removably inserted in the inset shaft receptacles of the shaft carrier. Specifically, the pipette shafts are provided with external threading on the upper end which can be screwed into the internal threading in the shaft receptacle.
The multiple channel pipetting device of the prior art is designed as an air buffer pipetting device, wherein the pipette tips, for ingesting liquid, are pushed onto the tip holder of the pipette shaft. The pipette holders are so smoothly designed on the surface, that the pipette tips can be directly sealingly pushed on. This results, however, in certain demands on the pipette tips.
Being an air buffer pipetting device, the above-mentioned multiple channel pipetting device naturally needs a circular plunger seal for the pipette plunger. Here, in each case, this is arranged on the upper end of the plunger receptacle facing the plunger carrier in the shaft carrier and is designed as a circumferential seal of elastomer material, namely an O-ring. The air volume relevant when pipetting is thus formed, on the one hand, by the cylinder in the pipette shaft, but moreover, also by the volume of the plunger receptacle between the pipette shaft and the plunger seal. The pipette shaft must then be sealingly screwed into the shaft receptacle in the shaft carrier. This requires special materials or an additional seal at this position.
Should just one channel of the above-mentioned multiple channel pipetting device have a leak, the entire pipetting device has to be taken apart because it is necessary to then be able to reach the plunger seal in the shaft carrier. Normally, it is not known if the leak comes from the plunger seal, from the seal between the pipette shaft and the shaft receptacle or from the seal between the pipette tip and the tip holder. Maintenance is work intensive and expensive.
Attaching a pipette shaft by means of a screw-cap has been known for decades (U.S. Pat. No. 3,732,735, DD 283 779 A) in respect to one channel pipetting devices. The thus existing undercut on the pipette shaft is used to provide a circular seal receptacle on the upper end of the pipette shaft in which the plunger seal is arranged. The plunger seal is affixed in this plunger receptacle by an affixing element which is provided with external threading to be screwed into the internal threading of the screw-cap. This construction is comparably work intensive and takes up so much space in the radial direction due to the screw-cap, that it can not be seen as suitable for the required stand measurements, in particular in micro titration stands.
The object of the teaching is thus, to make the maintenance of the known multiple channel pipetting device described above, which is also determined and suitable for low stand measurements, more user-friendly.
The object described above is met by a multiple channel pipetting device according to the invention in which each pipette shaft has a circumferential seal receptacle inside, at its upper end in which the circumferential plunger seal is positioned and in which the circumferential plunger seal, at least in the case of a pulled back pipette plunger, definitely remains in the seal receptacle when the pipette shaft is removed from the shaft carrier.
It has been recognized that it is practical for the maintenance of a multiple channel pipetting device of the sort described here, that all of the seals are provided on the pipette shaft. Should, namely, the plunger seal for the pipette plunger also be arranged in the pipette shaft, an additional seal between the pipette shaft and the shaft carrier is not needed because the air volume is confined to the pipette shaft. In this case, it comes to the simple measure, in the case of a leak, that only the pipette shaft has to be taken apart and exchanged without having to pay attention to which of the two sealsxe2x80x94plunger seal or pipette tip sealxe2x80x94is responsible for the leak. Nothing has to be completely taken apart or exchanged from the pipetting device, the problem is corrected by merely exchanging the pipette shaft.
The invention is based on the realization that above-explained concept can be achieved even with a multiple channel pipetting device where the shaft receptacles are inserted in the shaft carrier.
Moreover, the invention covers a pipette shaft for such a pipetting device, too.
In the following, the invention is explained more precisely with a drawing presenting merely one preferred embodiment.
FIG. 1 is a perspective view of an example of a multiple channel pipetting device of the present application;
FIG. 2a is a partial, mostly sectional view, of a multiple channel pipetting device according to the invention with two plungers arranged next to one another, assembled in a ready-to-use fashion;
FIG. 2b is a view corresponding to that of FIG. 2a, but with the pipette shafts partially unscrewed; and
FIG. 2c is a view corresponding to that of FIG. 2a, but with the pipette shafts completely unscrewed.